1. Field of Invention
This invention is generally related to systems and methods for determining the field of view of a sensor.
2. Description of Related Art
It is known in the art to provide developability sensors for analyzing toner-developed test patch areas. These test patch areas are generated on the surface of a photoreceptor of a xerographic image forming apparatus to obtain a measure of the image quality of that image forming apparatus.
The xerographic imaging process is initiated by charging a charge retentive surface, such as that of a photoconductive member, to a uniform potential. The charge retentive surface is then exposed to a light image of an original document, either directly or via a digital image driven laser. Exposing the charged photoconductor to light selectively discharges areas of the surface while allowing other areas to remain unchanged. This creates an electrostatic latent image of the document on the surface of the photoconductive member.
Developer material is then brought into contact with the surface of the photoconductor material to develop the latent image into a visible reproduction. The developer typically includes toner particles with an electrical polarity that is the same as, or that is opposite to, the polarity of the charges remaining on the photoconductive member. The polarity depends on the image profile.
A blank image receiving member is then brought into contact with the photoreceptor and the toner particles are transferred to the image receiving member. The toner particle forming the image on the image receiving member are subsequently heated, thereby permanently fixing the reproduced image to the image receiving member.
Electrophotographic or xerographic laser printers, scanners, facsimile machines and similar document reproduction devices must be able to maintain proper control over the systems of the image forming apparatus to assure high quality output images. For example, the level of electrostatic charge on the photographic member must be maintained at a certain level to be able to attract the charged toner particles. The light beam must have the proper intensity in order to be able to discharge the photoreceptor. In addition, the toner particles must be at the proper concentration to ensure high print quality. As the image forming apparatus continues to operate, changes in operating conditions will cause these parameters to vary from their initial values. For example, an increase in the humidity in the environmental conditions around the corona discharge device used to generate the electrostatic charge on the photoreceptor will cause a decrease in the magnitude of the charge that is ultimately placed on the photoreceptor.
Changes due to the variation in various operative components of the image forming apparatus impact print quality. Thus, it is desirable to monitor the operating parameters of the image forming apparatus to ensure proper operation of the image forming apparatus.
One way to control the many parameters that operate together as the image forming apparatus reproduces images is to use one or more process control patches strategically positioned on the photoconductive or charge-retaining member of the image forming apparatus. The one or more control patches are usually generated by sending a known pattern of data to control the modulation of the light emitting elements in an exposure station. Since the data patterns are known, the various system parameters, such as the electrostatic charge that must be present on the surface of the photoreceptor to create the developed resultant image, can be determined. The one or more control patches are deposited onto a small area of the photoreceptor between areas reserved for placement of the latent images. This area is called the interpage zone.
In existing xerographic print engines, sensor readings of toner control patches serve many purposes. One purpose is to provide a basis for adjusting the appropriate system parameters, such as corona charging and developer dispense rates to maintain print image quality. Another purpose is to provide a basis for identifying and declaring system fault conditions, such as a photoreceptor voltage which is too high or too low, i.e. a determination of whether a voltage reading is outside of a target voltage range.
Prior art techniques for accomplishing control of system parameters require a large number of toner patch readings resulting in a significant waste of toner. Thus, for system control, there is a strong desire to reduce the number of readings to the minimum required to adequately maintain the system parameters in order to conserve toner.
However, reducing the number and or size of test patches that must be produced is in some sense dependent on knowing the relative location of the field of view of a sensor, such as a densitometer, on the photoreceptor surface. Conventionally, the field of view of the sensor on the photoreceptor cannot be observed. As a result, conventionally, it was not possible to limit the size of the test patches to only that sufficient to fill the field of view of a sensor.
The invention provides systems and methods that locate a field of view of a sensor based on observations of disturbances created in the element being viewed with the sensor due to interactions between the sensor and the element.
This invention separately provides systems and methods that determine the location of a field of view of a sensor relative to a surface of a photoreceptor.
This invention further provides systems and methods that locate the field of view of a light-emitting sensor relative to the surface of the photoreceptor by observing the disturbances created in a test patch formed on the surface of the photoreceptor due to the light emitted by the sensor.
In various exemplary embodiments the systems and methods of this invention, a test patch is formed on a photoreceptor and passed past a light-emitting sensor. In normal operation, the light emitting sensor generally creates little disturbance in the test patch. The area of the test patch viewed by the sensor, which generally cannot extend beyond the area of the test patch illuminated by the sensor. According to the systems and methods of this invention, the light source of the sensor is driven sufficiently to create a measurable or observable disturbance in the test patch. In these embodiments, the is disturbance is a discharging of the charge on the photoreceptor used to create the test patch.
As a result, some toner previously attached to the discharged image area of a test patch region of the photoreceptor, that lies within the area illuminated by the sensor""s light source, is now electrostatically attracted to the discharged background area of the photoreceptor. The illuminated portion of the test patch thus contains a different distribution of toner than the non-illuminated portion. The location of this disturbed portion can be sensed or observed, either automatically or by a user. The extent and location of the test patch can thus be reduced to generally correspond to just the location of the disturbed portion of the test patch, and to generally about the same extent since the field of view of the sensor should lie within the illuminated area, and the illuminated area generally corresponds to the observed disturbed area, the location of the field of view of the sensor is determined.
These and other features and advantages of this invention are described in, or are apparent from, the following detailed description of various exemplary embodiments of the systems and methods according to this invention.